The molecular chaperones are found in all compartments of a cell where conformational rearrangements of proteins occur, and although protein synthesis is the major source of unfolded peptides in the cell, a challenge to the cell by high temperature or other stimuli that might render proteins structurally labile, and hence prone to unfolding and aggregation, is met with a specific cellular response involving the production of protective proteins. This response is a phenomenon observed in every cell type ranging from prokaryotes to eukaryotes and is referred to as the heat-shock- or stress-response. The proteins induced by this response are known as the heat shock proteins (HSPs), of which there exist several families.
A primary example of a family of chaperones is the Hsp70 proteins. This family has recently been implicated in other aspects of cellular homeostasis besides serving as a chaperone—most markedly through its anti-apoptotic features, its functions in immunity, and the apparent dependence of cancer cells on the upregulation of Hsp70. Furthermore, Hsp70 can serve a role in safeguarding lysosomal integrity.
The lysosomal storage diseases are a rare group of diseases, characterized by the accumulation of substances in the lysosomal compartment and resulting destabilization hereof, with a resulting devastating effect for affected individuals. Substances accumulate in the lysosomal compartment due to deficiencies in the enzymes involved in their catabolism. To this date, no treatment is available for most lysosomal storage diseases. The use of enzyme replacement therapy (ERT), by providing to a patient the recombinant enzyme that is deficient, has been employed for a subset of these diseases. However, ERT is a very expensive form of therapy which may limit its use in some areas, and also is effective only towards the specific type of disease to which the recombinant enzyme has been produced.
International patent application WO 2009/155936 is aimed at providing new means for treating lysosomal storage disorders by exploiting the newly identified interaction between Hsp70 and the lysosomal phospholipid Bis(monoacylglycero)phosphate (BMP) to promote lysosomal stabilization. This interaction was shown to reverse the pathology of lysosomal storage diseases which arise from a defect in an enzyme whose activity is associated with the presence of lysosomal BMP as a co-factor; such as Niemann-Pick disease and Farber disease.
The present inventors have now surprisingly found that HSP70 is also beneficial in reversing the pathology of lysosomal storage diseases which arise from a defect in an enzyme whose activity is not directly associated with the presence of lysosomal BMP as a co-factor; such as glycogen storage diseases, gangliosidoses, neuronal ceroid lipofuscinoses, cerebrotendinous cholesterosis, Wolman's disease, cholesteryl ester storage disease, disorders of glycosaminoglycan metabolism, mucopolysaccharidoses, disorders of glycoprotein metabolism, mucolipidoses, aspartylglucosaminuria, fucosidosis, mannosidoses, and sialidosis type II.